Xvi INTRODUCTION. 
by the constitutional state of the bird, and as that is in its 
highest degree of vigour immediately previous to the season 
of propagation, why may not such vigour be exhibited to the 
very extreme points of the circulating medium, by a partial 
variation of colour, or an increased lustre of tone in the for- 
mer hue of the feather? It is not fanciful, for it has been 
established as a maxim in Pathology, that the state of health 
may, in man, be ascertained by the occasional flaccidity or 
crispness of the hair; and have we not repeatedly met with 
well authenticated instances of great and sudden changes 
having taken place in its colour, under strong mental affec- 
tions, acting only, of course, through the organic structure of 
the body ? 
Changes of colour in the hair of many animals are seen, 
and that also at particular seasons; and (as Dr FLEmIne as- 
serts, in the case of the stoat, and some others, that assume a 
winter’s garb) without any actual shedding of their coat, either 
upon the first variation, or in regaining their summer’s hue. 
It is possible, and there is new some reason for believing, 
that the edges only of the feather may be shed (but not by 
a gradual process), thus presenting a newer and brighter 
surface, either of the same, or, more frequently, of a diffe- 
rent shade of colour. In the birds in which this partial 
change happens, it may even be observed, that, where the 
feather, as on the head of the Chaffinch, Reed-Bunting, and 
Stone-Chat, is of two distinct hues, the webs cf the exterior 
one are joined to the main body of the feather by a line of 
separation of finer texture, thus forming an adscititious mar- 
gin, as it were, to the inner part. 
